Intl

The Intl object is the namespace for the ECMAScript Internationalization API, which provides language sensitive string comparison, number formatting, and date and time formatting. The constructors for Collator, NumberFormat, and DateTimeFormat objects are properties of the Intl object. This page documents these properties as well as functionality common to the internationalization constructors and other language sensitive functions.

Methods

Locale identification and negotiation

The internationalization constructors as well as several language sensitive methods of other constructors (listed under See also) use a common pattern for identifying locales and determing the one they will actually use: they all accept locales and options arguments, and negotiate the requested locale(s) against the locales they support using an algorithm specified in the options.localeMatcher property.

locales argument

The locales argument must be either a string holding a BCP 47 language tag, or an array of such language tags. If the locales argument is not provided or is undefined, the runtime's default locale is used.

A BCP 47 language tag defines a language and minimally contains a primary language code. In its most common form it can contain, in order: a language code, a script code, and a country or region code, all separated by hyphens. While the tag is not case sensitive, it is recommended to use title case for script code, upper case for country and region codes and lower case for everything else.

Examples:

"hi": Hindi (primary language).

"de-AT": German as used in Austria (primary language with country code).

"zh-Hans-CN": Chinese written in simplified characters as used in China (primary language with script and country codes).

The subtags identifying languages, scripts, countries (regions), and (rarely used) variants in BCP 47 language tags can be found in the IANA Language Subtag Registry.

BCP 47 also allows for extensions. JavaScript internationalization functions use the "u" (Unicode) extension, which can be used to request additional customization of Collator, NumberFormat, or DateTimeFormat objects. Examples:

"de-DE-u-co-phonebk": Use the phonebook variant of the German sort order, which expands umlauted vowels to character pairs: ä → ae, ö → oe, ü → ue.

"ja-JP-u-ca-japanese": Use the Japanese calendar in date and time formatting, so that 2013 is expressed as the year 25 of the Heisei period, or 平成25.

"en-GB-u-ca-islamic": use British English with the Islamic (Hijri) calendar, where the Gregorian date 14 October, 2017 is the Hijri date 24 Muharram, 1439.

Locale negotiation

The locales argument, after stripping off all Unicode extensions, is interpreted as a prioritized request from the application. The runtime compares it against the locales it has available and picks the best one available. Two matching algorithms exist: the "lookup" matcher follows the Lookup algorithm specified in BCP 47; the "best fit" matcher lets the runtime provide a locale that's at least, but possibly more, suited for the request than the result of the Lookup algorithm. If the application doesn't provide a locales argument, or the runtime doesn't have a locale that matches the request, then the runtime's default locale is used. The matcher can be selected using a property of the options argument (see below).

If the selected language tag had a Unicode extension substring, that extension is now used to customize the constructed object or the behavior of the function. Each constructor or function supports only a subset of the keys defined for the Unicode extension, and the supported values often depend on the language tag. For example, the "co" key (collation) is only supported by Collator, and its "phonebk" value is only supported for German.

options argument

The options argument must be an object with properties that vary between constructors and functions. If the options argument is not provided or is undefined, default values are used for all properties.

One property is supported by all language sensitive constructors and functions: The localeMatcher property, whose value must be a string "lookup" or "best fit" and which selects one of the locale matching algorithms described above.